For making multiple-fold umbrella, the weight of the rib assembly is expected to be decreased as much as possible. If all ribs of the rib assembly are made of aluminum alloy, the umbrella weight can be greatly reduced. However, the aluminum rib may be easily deformed or broken when subjected to strong wind.
U.S. Pat. No. 5,931,175 to the same inventors of this application disclosed a top rib (1) made of light materials including aluminum alloy and an outer rib (2) made of composite or plastic materials for forming a rib assembly especially adapted for making a single-fold umbrella. However, it did not disclose a rib assembly for making triple fold or multiple-fold umbrella.
The present inventor has found the drawbacks of the prior arts and invented the present rib assembly for multiple-fold umbrella having a plastic intermediate rib interconnected among other light ribs.